Various techniques including Machine-to-Machine (M2M) communication and various devices including a smart phone requiring a high data rate, a tablet Personal Computer (PC), etc. have emerged and gained popularity. As a consequence, the amount of data to be processed in a cellular network is rapidly increasing. To satisfy the ever-increasing data processing requirement, Carrier Aggregation (CA), cognitive radio, etc. for efficiently using more frequency bands, and Multiple Input Multiple Output (MIMO), Coordinated Multipoint transmission and reception (CoMP), etc. for increasing the amount of data transmitted in limited frequencies have been developed. Also, communication environment is evolving toward an increased density of nodes accessible to User Equipments (UEs). A node refers to a fixed point with one or more antennas, which may transmit or receive wireless signals to or from a UE. A communication system with densely populated nodes may provide a high-performance communication service to UEs through cooperation between nodes.
In this multi-node cooperative communication scheme in which a plurality of nodes communicate with a UE using the same time-frequency resources, each node operates as an independent Base Station (BS) and thus offers a higher throughput than in a conventional communication scheme in which a node communicates with a UE without cooperation from other nodes.
A multi-node system performs cooperative communication using a plurality of nodes each operating as a BS, an Access Point (AP), an antenna, an antenna group, a Radio Remote Header (RRH), or a Radio Remote Unit (RRU). Compared to a conventional centralized antenna system in which antennas are concentrated in a BS, the plurality of nodes are generally apart from each other by a predetermined distance or larger in the multi-node system. The plurality of nodes may be managed by one or more BSs or one or more BS Controllers (BSCs) that control an operation of each node or schedule data to be transmitted or received through each node. Each node is connected to a BS or BSC that controls the node by cable or a dedicated line.
[5] The above-described multi-node system may be regarded as a MIMO system in the sense that distributed nodes may communicate with one or more UEs by transmitting or receiving different streams at the same time. However, since signals are transmitted using nodes distributed to various locations, each antenna covers a reduced transmission area in the multi-node system, relative to antennas in the conventional centralized antenna system. As a result, each antenna may need a reduced transmission power in transmitting a signal in the multi-node system, compared to a conventional system that implements MIMO with a centralized antenna system. In addition, as the transmission distance between an antenna and a UE is reduced, path loss is decreased and high-rate data transmission is possible. Accordingly, the transmission capacity and power efficiency of a cellular system may be increased and communication may be conducted with uniform quality irrespective of the locations of UEs within a cell. Further, the multi-node system boasts of reduced signal loss during transmission because a BS(s) or BSC(s) connected to a plurality of nodes cooperate in data transmission and reception. If nodes apart from each other by a predetermined distance or larger conduct cooperative communication with a UE, correlation and interference between antennas are decreased. Consequently, the multi-node cooperative communication scheme achieves a high Signal-to-Interference plus Noise Ratio (SINR).
Owing to these advantages of the multi-node system, the multi-node system has emerged as a promising basis for cellular communication by substituting for the conventional centralized antenna system or operating in conjunction with the conventional centralized antenna system in order to reduce BS deployment cost and backhaul maintenance cost, extend service coverage, and increase channel capacity and SINR.